1. Field of the Invention
The present invention relates to hybrid electric vehicles (HEVs). In particular, the present invention relates to HEVs having an electric assist bus electrically coupled to an accessory load bus.
2. Background Art
A hybrid electric vehicles (HEV) is an example of a vehicle having an electric assist bus and an accessory bus.
The electric assist bus electrically couples an energy source to an electric motor. The electric motor converts electric energy to mechanical energy to provide motoring torque for use in moving the vehicle and converts mechanical energy to electric energy to capture kinetic energy otherwise dissipated during braking. The use of the electric motor to provide motoring torque is commonly referred to as electric assist. The use of the electric motor to provide braking torque is commonly referred to as regenerative braking.
The accessory load bus electrically couples accessory loads to an alternator. The electrical energy provided by the alternator is transferred over the accessory load bus for use by the accessory loads. The accessory loads typically operate best within a predefined voltage range. Accordingly, it is desirable to maintain the accessory load bus within the predefined voltage range.
Electric assist and regenerative braking tends to induce voltage variations on the electric assist bus. Such voltage variations can become problematic if the accessory load bus is electrically coupled to the electric assist bus. In this case the accessory loads may experience the voltage variations and associated malfunctions or other damage.
In the past, the electric assist bus was electrically isolated from the accessory load bus to protect the accessory loads from the induced voltage variations. Electrically isolating the accessory load bus from the electric assist bus has some drawbacks. Namely, systems having such isolated busses tend to be less efficient than systems which electrical couple the busses. As such, there exists a need to electrically couple the accessory load bus to the electric assist bus.